[PATCH] manifest: remove unused property _oldmanifest

[Martin von Zweigbergk]

# HG changeset patch
# User Martin von Zweigbergk <martinvonz at google.com>
# Date 1494261561 25200
#      Mon May 08 09:39:21 2017 -0700
# Node ID f7920a409fb0516b7dc48404537b1fd24cf8e23e
# Parent  8f1a2b848b52ea7bf3fe2404e3b62924c7aae93f
manifest: remove unused property _oldmanifest

The last use seems to have gone away in 7c7d845f8b64 (manifest: make
manifestlog use it's own cache, 2016-11-10).

diff --git a/mercurial/manifest.py b/mercurial/manifest.py
--- a/mercurial/manifest.py
+++ b/mercurial/manifest.py
@@ -1317,8 +1317,7 @@
             cachesize = opts.get('manifestcachesize', cachesize)
         self._treeinmem = usetreemanifest
 
-        self._oldmanifest = repo._constructmanifest()
-        self._revlog = self._oldmanifest
+        self._revlog = repo._constructmanifest()
 
         # A cache of the manifestctx or treemanifestctx for each directory
         self._dirmancache = {}